1. Field of the Invention
The present invention relates to a surface discharge type plasma display panel and its manufacturing method, and a surface discharge type plasma display device. Especially, the present invention is directed to a structure of barrier ribs and a technique for forming the barrier ribs.
2. Background of the Invention
FIG. 60 is a block diagram showing a plasma display panel device, for example, as disclosed in FIG. 1 of Japanese Patent Laid-Open Gazette P5-307935A or in FIG. 14 of U.S. Pat No. 5,661,500. In FIG. 60, the reference character 100P indicates a plasma display device; 1P indicates a plasma display panel (hereinafter referred to as a PDP) including X and Y display electrodes (hereinafter referred to as X and Y electrodes, respectively) and an address electrode (hereinafter referred to as an A electrode); 110P indicates a scan control portion; 120P indicates an A/D converter for converting an input signal from analog to digital (hereinafter referred to as an A/D); 130P indicates a frame memory for storing an output of the A/D 120P; 141P indicates an X-electrode driving circuit for providing a driving signal to the X electrode of the PDP 1P; 142P indicates a Y-electrode driving circuit for providing a driving signal to the Y electrode of the PDP 1P; 143P indicates an A-electrode driving circuit for providing a driving signal to the A electrode of the PDP 1P. The reference character 2P indicates a drive control system consisting of the A/D 120P, the frame memory 130P, the scan control portion 110P, the X-electrode driving circuit 141P, the Y-electrode driving circuit 142P, and the A-electrode driving circuit 143P.
FIG. 61 is a perspective view showing the outline of a sectional structure of the conventional PDP 1P, for example, as disclosed in FIG. 3 of Japanese Patent Laid-Open Gazette No. P5-299019A or in FIG. 2 of U.S. Pat. No. 5,661,500. In FIG. 61, the reference numeral 211 indicates a first substrate which is a front substrate; 217 indicates a dielectric layer covering the X and Y electrodes; 218 indicates a protective layer formed of MgO or the like, for covering the surface of the dielectric layer 217; 222 indicates an A electrode extending along a second direction orthogonal to a first direction which will be described later; 221 indicates a second substrate which is a rear substrate; 228 indicates a phosphor formed in stripes along side walls of barrier ribs 229 which will be described later, without interruption; 229 indicates a barrier rib formed in parallel along the second direction on the second substrate 221 and separated from each other; and 230 indicates a discharge space filled with discharge gas (Penning gas) including Xe atoms for emitting ultraviolet rays to be absorbed into the phosphors 228. Further, 241 indicates a strip transparent conductive film consisting of a tin oxide film or the like, and extending in parallel along the first direction at a predetermined interval (discharge gap) so as to constitute X and Y electrodes XEP and YEP; and 242 indicates a strip metal film for supplementing conductivity of the strip transparent conductive film 241, consisting of multiple films such as Cr--Cu--Cr or Cr--Al--Cr. Each of the X and Y electrodes XEP and YEP consists of the strip transparent conductive film 241 and the strip metal film 242 added to the strip transparent conductive film 241. The reference character EGP indicates one pixel consisting of three unit luminescent areas EUP emitting red light (R), green light (G), and blue light (B), respectively, (indicated by EUP.sub.R, EUP.sub.G, EUP.sub.B, respectively, in FIG. 61) for a color display device. The reference character SP indicates a display surface.
Next, operation of the conventional plasma display device 100P will be described. The plasma display device 100P consists of the PDP 1P, and the drive control system 2P electrically connected to the X, Y, and A electrodes of the PDP 1P via a flexible printed circuit board (not shown).
In the drive control system 2P, an input signal VINP for providing image data is first converted from analog to digital by the A/D 120P, and digital data outputted from the A/D 120P is stored into the frame memory 130P. Then, the scan control portion 110P accesses the digital image signals stored in the frame memory 130P, and on the basis of the signals, outputs various control signals for controlling drive of the X-electrode driving circuit 141P, the Y-electrode driving circuit 142P, and the A-electrode driving circuit 143P to the corresponding circuits 141P to 143P, respectively. Upon receipt of the control signals, the driving circuits 141P to 143P apply driving pulse signals such as priming pulses, write pulses, or discharge sustain pulses to their corresponding electrodes, which drives the PDP 1P.
The PDP 1P is a three-electrode, surface discharge type PDP where a pair of display electrodes (the X and Y electrodes XEP and YEP) and the A electrode 222 correspond to the unit luminescent areas EU, respectively. Each of the X and Y electrodes XEP and YEP consists of the strip transparent conductive film 241 and the strip metal film 242, and it is arranged on the inside surface of the first substrate 211 on the side of the display surface SP.
On the other hand, the barrier ribs 229 are provided in strips on the second substrate 211. A height h of the barrier ribs 229 specifies a height of the discharge space 230. The discharge space 230 is sectioned per unit luminescent area EUP along an extending direction of the X and Y electrodes XEP and YEP, that is, along the first direction.
On the inside surface of the second substrate 221 between the adjacent barrier ribs 229 formed in parallel with each other, the A electrodes 222 of a predetermined width are arranged by printing and firing a pattern of a silver paste. Further, except where the barrier ribs 229 are in contact with the protective layer 218 and its vicinity, the phosphors 228 emitting red light R, green light G, blue light B, respectively are provided so as to cover the inside surface of the second substrate 221.
Accordingly, in the PDP 1P, the continuous stripe phosphors 228 are provided almost on the whole inside surface of the second substrate 221 including both side surfaces of the barrier ribs 229 and the surface of the A electrodes 222.
Further, in some cases, a layer (black stripe) using a low melting point glass with a black pigment added, for example, may be provided on the inside surface of the first substrate 211 in order to prevent deterioration in image contrast due to extraneous light entering from outside through the first substrate 211 forming the display surface SP.
The aforementioned conventional technique, however, contains some problems. For easy understanding of one of those problems, a logic of phenomena of the discharge and the propagation of ultraviolet rays will be described schematically with reference to FIG. 62.
On occurrence of discharge (especially display discharge) between the X and Y electrodes, Xe atoms included in discharge gas are excited and emit 147 nm ultraviolet rays. This emission of ultraviolet rays occurs when Xe atoms of resonance level return to their ground level, accompanied with what is called "self absorption". The "self absorption" is a phenomenon that the ultraviolet rays once emitted from the Xe atoms are absorbed by different Xe atoms being at a ground level, and the different Xe atoms are excited.
These excited different Xe atoms will also emit ultraviolet rays of the same wavelength when returning to their ground level. By repeating the self absorption and the emission of ultraviolet rays in this way, the 147 nm ultraviolet rays propagate and diffuse at random within the discharge space. FIGS. 62A and 62B schematically show this self absorption of ultraviolet rays.
Since the ultraviolet rays propagate and diffuse within the discharge space as described above, the expansion of ultraviolet rays due to the gas discharge between the X and Y electrodes far more reaches than both physical widths of the X and Y electrodes. FIG. 63A schematically shows the expansion of ultraviolet rays when gas discharge occurs between any X and Y electrodes XEP and YEP located in an upper portion of the space which extends along the second direction and is surrounded by the adjacent barrier ribs 229, the phosphors 228, and the protective layer 218 as described above. Further, FIG. 63B schematically shows luminance on the side of the first substrate 211 at that time, where the horizontal axis indicates a distance from the center of discharge gap (substantially corresponding to the center of a display line D).
The discharge between the X and Y electrodes XEP and YEP generates ultraviolet rays as described above, and the ultraviolet rays are propagated and diffused by the self absorption and emission. In this case, since the adjacent barrier ribs 229 are in parallel with each other as shown in FIG. 61, the occurrence of the gas discharge is spatially limited only in the second direction along the A electrode 222. Thus, as schematically shown in FIG. 63B, the distribution of luminance extends along the second direction. The metal electrodes 242, however, do not transmit light from the phosphors 228, so that the display light can not propagate to an area positioned right over the metal electrodes 242. Thus, the distribution of luminance to be observed breaks at positions corresponding to places where the metal electrodes 242 are formed.
A correlation between gas discharge and luminescence state will be further described with reference to FIG. 64. FIG. 64 is a plan view schematically showing the positioning of each unit luminescent area EUP, the barrier ribs 229, and the phosphors 228. In FIG. 64, the phosphors emitting red light R, green light G, and blue light B are denoted by the reference characters 228R, 228G, and 228B, respectively.
As shown in FIGS. 63A and 63B, on the occurrence of the gas discharge between the X and Y electrodes XEP and YEP, the Xe atoms included in the discharge gas are excited and emit ultraviolet rays. The ultraviolet rays are incident on the facing phosphors 228, which causes luminescence (generation of visible light) from the phosphors 228. The phosphors 228 themselves are almost white against the visible light, so that the visible light is hardly absorbed by the phosphors 228. Thus, luminescence emitted from the phosphors 228 is reflected on the surface of the phosphors 228. The barrier ribs 229 also consist of materials for reflecting luminescence. The emitted luminescence does not leak into the unit luminescent areas EUP adjacent to each other with respect to the first direction D1 and emitting luminescence of different colors, because the phosphors 228 are provided in generally U-shaped consecutive stripes along the second direction D2 and the adjacent barrier ribs 229 extending along the first direction D1 prevents the phosphors 228 from emitting in the first direction D1. However, the emitted visible light reflects on the surface of the phosphors 228, and consequently leaks into the unit luminescent areas EUP adjacent to each other with respect to the second direction D2 and emitting luminescence of the same color as shown in FIG. 64, because only the generally U-shaped consecutive stripe phosphors 228 of white color exist in the way along the second direction D2. In FIG. 64, the hatched blocks show the propagation region of luminescence emitted from each unit luminescent area.
In this manner, the leakage of luminescence may color a pixel to be generally white, for example, by red because of red light leaked from the adjacent unit luminescent area EUP of the adjacent pixel. Namely, the leakage of luminescence from a pixel of the next line to a pixel of the previous line gives an adverse effect on the pixel of the previous line.
As described above, a conventional display device involves some problems due to the propagation and diffusion of ultraviolet rays:
Conventional Problem (1): While the self absorption and emission of ultraviolet rays are repeated, the excited Xe atoms may be ionized. In this case, a loss increases with the number of repetitions, which deteriorates luminous efficiency.
Conventional Problem (2): The ultraviolet rays may be absorbed by the protective layer 218 in the course of the phenomenon of the self absorption and emission of ultraviolet rays occurring along the barrier ribs 229 to thereby cause loss of ultraviolet rays. In this case, loss increases with increasing traveling distance of the phenomenon, which deteriorates luminous efficiency.
The aforementioned conventional problems (1) and (2) are raised in the aspect of luminous efficiency. Further, from the viewpoint of the leakage of luminescence as described with reference to FIG. 64, the following other problems are presented.
Conventional Problem (3): Between pixels EG adjacent to each other with regard to the second direction D2, luminescence generated at each adjacent display line leaks into its adjacent unit luminescent area EUP of the same color. This leakage of luminescence makes it difficult to hold a required pixel dimension and to achieve image display with required luminance at each of adjacent display lines, especially affecting color balance of a combination of primary colors to be used in a standard color display.
Further, another problem comes up in manufacturing a high-resolution plasma display device so as to keep up with the increase in pixel density.
Conventional Problem (4): When luminescence occurring at each unit luminescent area EUP extends over different unit luminescent areas of adjacent pixels as shown in FIG. 64, as a space between the adjacent display lines decreases, leakage of discharge tends to occur between the display lines (hereinafter referred to as discharge between cells) as schematically shown by circles with hatching in FIG. 65. This changes a stock of wall charges between cells where gas discharge occurred from its original state, hindering display operation. Further, unnecessary discharge may be caused or no display discharge may not be induced by the leakage of discharge associated with the achievement of high resolution.
Such influence of discharge between cells increases as increasing applied voltage in display operation or decreasing pitch between electrodes, which presents an obstacle to the increase in pixel density of PDP1.